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AIR CONDITIONING & HEAT PUMP SYSTEMS
AGE of AIR CONDITIONERS & HEAT PUMPS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
CLEANING & Legionella BACTERIA
COOLING LOAD REDUCTION by ROOF VENTS
CRITICAL DEFECTS on A/C SYSTEMS
DEFINITION of Heating & Cooling Terms
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM NOISES
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATOR COIL or COOLING COIL
EVAPORATIVE COOLING SYSTEMS
GAUGE, REFRIGERATION PRESSURE TEST
HEAT LOSS (or GAIN) in buildings
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR & DIAGNOSTIC FAQs for A/C
RETROFIT SIZING for A/C or HEAT PUMPS
WATER COOLED AIR CONDITIONERS
Air conditioner compressor unit diagnosis & repair guide: this article discusses the outdoor components of air conditioners and heat pumps: how the air conditioning compressor-condenser unit works; the detection of defects in air conditioning compressor and condensing units, including evaluation of air conditioner compressor noises, hard starting, lost cooling capacity, and detection of a burned out compressor or A/C compressors at or near end of their life. Maintenance tips including attention to compressor support pads and avoiding air conditioning refrigerant leaks are also addressed.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
What is the "Compressor" unit in an air conditioner or heat pump system?
What is the Average Life of an Air Conditioning or Heat Pump Compressor ?
See INSPECTION CHECKLIST - OUTDOOR UNIT for a simple checklist for the outdoor compressor/condenser unit. Also see DIAGNOSE & FIX AIR CONDITIONER / HEAT PUMP where we include some suggestions for diagnosing compressor or condenser fan and coil problems that can mean intermittent or totally lost cooling capacity of your system. Initial, simple diagnostic checks of the air conditioning compressor are also described at Compressor failure diagnosis. For a discussion of the indoor components of an air conditioning or heat pump system see AIR HANDLER / BLOWER UNITS.
If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
How the Air Conditioning Compressor/Condenser Unit Works to Move Heat from Indoors to Outside
The A/C Compressor: The air conditioning compressor motor is a pump which draws sensible heat laden refrigerant gas from the building's indoor components (evaporator or "cooling coil" in the indoor air handler) through the larger diameter refrigerant suction line into the compressor where that pump compresses the low pressure refrigerant gas to high pressure and higher temperature.
Raising the coolant (refrigerant) temperature above outdoor ambient temperature causes heat to flow from the coolant (flowing out of the compressor and through the outdoor A/C condenser coil) into outdoor air. (Heat always flows from warmer to cooler substances).
Sketch courtesy of Carson Dunlop Associates.
As we explain at THERMOSTATIC EXPANSION VALVES, it is the flow restriction provided by a cap tube or by a TEV in the refrigerant piping system that allows the A/C compressor pump to raise the system pressure and thus increase the temperature at which the coolant changes state. In other words, the TEV or cap tube allows the compressor to reduce refrigerant pressure on the LOW side of the metering device and raise refrigerant pressure on the HIGH side of the metering device.
Incidentally, A/C compressors can only accept and compress refrigerant in gas form. In fact the refrigerant vapor is superheated to be sure that there is no liquid at the pump - lest the pump be damaged. If liquid refrigerant were to flow into the compressor motor it would most likely cause catastrophic damage.
Definition of an Air Conditioner or Heat Pump
An air conditioner or heat pump compressor is a basically a motorized pump which moves refrigerant gas from the indoor cooling coil (where it has evaporated to cool indoor air blowing over that coil) to the outdoor compressor/condenser where the gas is compressed and cooled back to a liquid form. Refrigerant gas moves from the indoor air handler cooling coil to the outdoor compressor via the larger refrigerant "suction line". Liquid refrigerant returns from the outdoor compressor/condenser to the in-building air handler and evaporator coil. Evaporating liquid refrigerant inside the indoor cooling coil cools and dehumidifies indoor air. Condensing refrigerant gas outdoors at the compressor/condenser effectively is moving heat from indoors to the outdoor air. [During heat pump "heating" cycles the process is reversed, moving "heat" from outdoor air to the indoor coil.]
Heat pumps are described separately and in more detail at HEAT PUMPS.
What are the Components of the Outdoor Portion of a Central Air Conditioning System - the Air Conditioning Compressor Unit?
All of the above-listed air conditioner or heat pump components are discussed in detail throughout this website using the links at the left of these pages.
Air Conditioner or Heat Pump Compressor Unit Safety, Damage, & Environmental Warnings
Using Carrier installation instructions for the Carrier 24ANA unit as an example  and quoting:
Minimum Air Conditioner Compressor Unit Observations for an Air Conditioner Home Inspection Report
Example home inspection report language for an air conditioning compressor:
Sealed compressors cannot be opened for repair in the field and are normally replaced entirely when needed.
The diagnosis of a sealed compressor relies on external observations and measurements such as current draws (amps) of the compressor motor and the operating pressures the equipment can achieve.
While a sealed hvac compressor unit can't be field-repaired, the unit can be replaced as an entire system, and in some cases the damaged unit can be traded in for an allowance on the replacement compressor.
What are those three tubes seen welded or soldered to the hermetically sealed HVAC compressor can? There are three tubes you'll find on a typical sealed compressor unit:
Watch out: if you are carrying a refrigerator or freezer in other than upright position, that is if you have to place the unit on its side, place it so that the low side (suction side) refrigerant lines are facing "up" so as not to drain oil or liquid refrigerant into a line where it does not belong and where it may block a cap tube.
If you make a mistake and carry the appliance in the wrong position, you would be smart to leave it in the upright or operating position for a few hours before turning it on to avoid forcing a slug of oil into (and blocking) the CAPILLARY TUBES often used on home refrigerators or freezers. Leaving the system upright allows oil that may have leaked into the refrigerant line to drain back into the compressor motor. If you turn on the system too soon the risk is that you push this oil into the cap tube where it may remain or be hard to get out or worse, you may leak oil into the reed valves where they will be damaged when the compressor motor is turned on.
Open type refrigeration compressors
Open type refrigeration compressors are commonly found on automotive air conditioning systems. The motor that drives the actual compressor (the mechanical engine that compresses refrigerant gas) is physically separate from the compressor and is located outside of it. Typically a motor drives the compressor via a belt and pulley system (cars and some commercial refrigeration systems).
This is why you should run your automobile air conditioner from time to time even out of the cooling season - to lubricate the shaft seal around the compressor motor/pulley - that's a spot where refrigerant may leak out at a dried seal.
Semi-sealed HVAC compressors
Semi-sealed compressors can be disassembled and repaired, as can the open type above.
All compressors have a suction and a discharge valve to control refrigerant flow through the unit.
Reed Valve refrigeration compressor motors
Often the valve is a reed design - in which case the bottom reed is the intake valve and a top mounted reed is the discharge reed or valve that discharges out through a noise muffler into the condenser piping and coil.
It is these valves that can be destroyed if liquid refrigerant is sent through the compressor.
Rotary valve refrigeration compressor motors - Frigidaire rotary compressor motors
Some other refrigeration compressor valve designs are quite different from these simple reeds, including an old and very successful eccentric crank system: the rotary compressor motor design patented by Frigidaire™ and used in refrigerators for several decades.
This compressor motor design was used in a range of Frigidaire equipment and appliances including refrigerators and some air conditioners. The durability of the design stems at least in part from its simplicity: a simple eccentric crank (see our sketch at left) is the only moving part in the motor.
On this compressor motor the inlet or suction line is generally found on the bottom of the unit, feeding directly into the bottom of the piston assembly and sealed from the rest of the chamber. The interior of the compressor chamber (sketch note and arrow at left) is on the HIGH side of the system. So service valves, if they are installed at all, are placed on the high side of the system there.
Frigidaire eccentric crank rotary refrigeration compressor motors were remarkably durable and reliable - we used a salvaged Frigidaire refrigerator compressor as our HVAC service vacuum pump for many years.
Refrigeration compressor motors use 300 viscosity oils when working with refrigerants in the Freon family and 150 viscosity oils when working with other refrigerants. These are special oils that use a non-wax base such as Texaco Capella oil or oils by Virginia Chemical.
The refrigeration oil lubricates the moving parts of the compressor motor as it receives and compresses refrigerant gases. At Types of air conditioner or heat pump compressors & compressor designs when we warned that carrying a refrigerator or freezer on its side could drain oil out of the compressor motor into the refrigerant lines where it might later become a problem by blocking the capillary tube or might enter reed valves causing valve damage, this is the oil we were talking about.
If your air conditioning system won't work, follow these easy A/C-heat pump diagnostic guides
Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.
If your air conditioning or heat pump system has lost its cooling capacity or won't start, or if your air conditioning electrical bill has increased even though the system "on" time has not changed, select one or more of the diagnostic articles listed below.
Frequently Asked Questions (FAQs) about Air Conditioner or Heat Pump or other refrigeration system Compressor/Condenser UnitsBeginning at COMPRESSOR & CONDENSING COIL, A/C see the articles at Related Topics for detailed HVAC compressor/condenser troubleshooting and repair procedures. We include more general compressor/condenser questions just below.
Question: compressor just runs for a few seconds, then cuts off; short cycling A/C compressor problems
My condenser starts for a few seconds then cuts off cycle continues - Anon.
my compressor fun has started to short cycle, it run for 2-3 min then shuts off for one second then restarts runs again then stops etc. with no funny sounds or noises - Don
It's not clear from your question where in the entire cooling system your unit's troubles begin, so I'd look at diagnostic tips that may explain your compressor/condenser short cycling are found at LOST COOLING CAPACITY. Certainly a compressor that is having trouble starting can be diagnosed at HARD STARTING COMPRESSOR MOTORS, if you're sure the trouble is outside.
Question: ice on the refrigerant line, no cooling in the house
My line set going to outdoor unit has ice on it. Lost cooling in house. What is the problem and is there anything I can do to fix the issue - Pat
Reply: check the indoor air handler for an ice-blocked coil
A problem with a refrigerant metering device (thermostatic expansion valve, capillary tube, etc), or even a dirty air filter can lead to improper metering of refrigerant into the indoor cooling coil, leading to icing; but other causes of ice formation include an improper refrigerant charge or even something as simple as missing refrigerant line insulation. But when you also lose cooling inside, I suspect an ice blocked coil. See FROST BUILD-UP on AIR CONDITIONER COILS
Question: ice build up inside the ductwork
I have ice build up on the inside of the furnace duct work. This will plug up the lines and the fans will not circulate thus stop blowing cold air
If you find ice build-up inside the ductwork itself that's pretty unusual except in winter in freezing climates when moist air is rising into the duct system. Usually ice forms at the cooling coil in an air conditioner air handler or blower unit.
Question: My A/C unit kept blowing a fuse, now nothing runs
My Center A/C unit had a tuned up. I clean the evaporator, I put the blower down and put the new motor and clean the blades deeply, I have a clean filter, I clean the condenser deeply, and I bought a new thermostat. OK. The unit star running normally and you fill the normal warm air in the fan (outside) But 3 to 5 minutes later the heat in the condenser air increased suddenly the condenser stop with noise, and I need to turn it off. what is this? Please give me a clue? - Anon 6/28/22
I have a pretty old Tappan unit, and when the power goes out, if the A/C is running it will blow the fuse, usually we just replace the fuse, and now nothing will run on the A/C unit. any ideas? - Shantel 6/20/11
Question: My hi line is cold, low line is warm and the condenser blows hot air
In my situation the high pressure line is colder than the low pressure line. The condensor coil blows mainly hot air, but the end closest to the compressor blows hotter air than the end furthest from the compressor line. Any suggestions? - Jim T. 7/13/11
Mundo suggested: hey jim t check for restriction at the evaporator
Question: water comes out of my system when I turn on the A/C
When i turn on the (AC Outside unit Lennox ) there is an overflow of water in my basement at the furnace which is a gas furnace- Don 7/24/11
Don if you see water in your basement at the A/C unit when it's on, your condensate drain or pump is not working.
Question: No water is coming out of the condensate drain
water is not going through the drain hose - Anon 7/20/12
Question: Is the problem with the fan motor or the compressor motor in my condenser unit?
I've a Lennox outside a/c unit. The fan/motor and compressor are part of the unit. The fan was not spinning and the A/c is not running. I've isolated the problem down to the fan/motor or the compressor, but don't know how to check or find out which it is. Any idea on how to check if the fan/motor is 'bad' or the compressor is 'bad'? - Fan or ... 7/23/11
Fan or compressor: you could also have a bad control board, or relay switch in the compressor/condenser unit. If the fan is bad and the compressor is OK you'll hear the compressor turn on at the start of a cooling cycle, though a bad fan and system overheating could later cause some compressors to turn themselves back off. Similarly, if the compressor is bad your fan motor would still run. So I'm suspecting a control or switch problem./
Question: Our new AC won't keep running
uhm my A/C compressor broke about two weeks ago, we got a new one but when the fan starts the compressor works for a while and then it shuts down, and its turning on and off and i dont know whats wrong - Help. 7/25/11
Help: if your new A/c won't keep running after it has just been installed, surely you should call the installer and expect it to be repaired under warranty - it's just been two weeks.
Question: My AC won't work if I set the temperature down below 25C
my a/c is working properly when it is adjusted at 25 degree temprature, but if it is lower than 25, the compressor is disconnected by the overload protection. what is the problem with my a/c. - Mohamed 8/5/11
Mohamed an A/C compressor may cut off on thermal overload due to overheating from local conditions around the compressor/condenser unit (no shade, very hot weather), an older motor that is failing, a start capacitor problem, or even a refrigerant metering device problem. If there's nothing obvious to you, I'd get a service tech to take a look. Keep us posted.
Question: Icing at the compressor; compressor not turning on?
the outside unit of the heat pump is icing up on the compressor - Steve 8/7/11
Hi my fan in my house goes on but my compressor unit does not all the electric seems to be fine . could it be my thermostat? - Sam 8/7/11
the accu very heat,although it is new gen. clean,2Tr LS-60psi & HS-100psi, - Anon 8/6/11
Steve: icing at the compressor/condenser sounds like a refrigerant charger or refrigerant metering problem.
Question: My A/C compressor just won't stop running
I recently noticed my AC condenser unit still running when the system inside shutoff by itself. and also, does the condenser unit have to be leveled. I notice the slap which holding the unit is slopping. Any suggestions? Thank you. - Rick 8/16/11
A/C compressor/condenser won't stop running:
Question: can the condenser get oil logged
can a condenser become oil logged, how and why? - Dominic 8/22/11
Dom, it is normal for some refrigerant oil to circulate through the HVAC refrigeration system; Oil logging can occur in some installations if the refrigerant piping is not properly routed or due to an improper charge. The more usual problem is not at the condenser coil but at smaller orifices such as a cap tube or the TEV.
Question: our A/C compressor tries to start but then shuts right back off
I turned my AC on and noticed it wasn't getting cooler inside, I went out to the condensing unit and the compressor tries to kick on but then shuts right back off. Can not having enough refrigerant cause this? If not what's the deal? - Derek 8/22/11
Derek, as another reader commented, your compressor/condenser may be having trouble starting. A start capacitor can sometimes fix this problem and give some added life to the unit.
Question: compressor starts, fan doesn't start, I hear a hissing
My compressor turns on but the fan does not turn(Ican turn the blades by hand) within 10 t0 15 seconds I get a long a loud hissssssssssssssssssssss.
I HAVE SOME MORE INFO ON MY A/C WHEN THE A/C IS TURNED ON BY DROPPING THE TEMP IN THE HOUSE THE COMPRESSOR TURNS ON BUT THE FAN DOES NOT TURN, IF YOU START TO TURN THE FAN BY HAND IT STARTS SPINNING. WHEN I TURN IT OFF BY PICKING UP THE TEMP IT STOPS. WHEN I DROP THE TEMP AGAIN NOTHING GOES ON. IF I WAIT A FEW MINUITES AND TRY IT AGAIN THE COMPRESSOR STARTS BUT THE FAN STILL HAS TO BE STARTED BY HAND. THANKS FOR ANY HELP YOU CAN GIVE...
Henry I suspect a bad fan start-run capacitor.
Question: no air is coming out of our supply registers
I have a coleman unit. Had heating probs 2 years ago leading to complete computer panel replaced, evaporator coils cleaner, gas regulator replaced. Two days ago, my A/C decided to stop working. I hear the freon flowing into the coil region, the fan outside is turning, but no air is coming out of registers. What can it be? - Cheryl 9/9/11
Cheryl if you have no air coming out of supply registers the blower fan is not working or the duct system has become disconnected or blocked. Coil ice-over in the air handler can also block airflow. Start by determining that the blower is running and that the air filter is clean.
Question: water at the air return vent
what makes the water from an airconditioner build up in the return vent? - Connie Woyan 9/15/11
Connie: if you see water at the return vent it may be condensation on a cool surface, or it could be condensate leaking down into the return vent from your air handler. You'll need to make a closer inspection of the air handler (blower unit) itself.
Question: what type of copper is used in HVAC refrigeration piping or tubing?
What is the content of copper tubes used in AC? (i.e I would like to know the contents of pipe which is being connected between the Fan and compressor of split AC) - Pratik Shah 10/1/11
Question: no sweat on the suction line
what could be the problem when the sunction line of an air conditioner is not sweating? - Diana 2/3/12
Question: hard starting compressor
jon- ac system is less than a year old, when I turned on ac to check, condensor comes on then shuts back off, then 30-45 seconds after comes on again for 2-5 seconds. Whats wrong? - Jon Anon 8/18/12
Compressor on Lennox centeal air not turning even if the thermostat is activated.. It is blowing warm air.
Anon: regarding your hard-starting compressor/condenser unit: we can't with confidence say what's wrong with so little information - your service tech can diagnose the problem, probably fairly quickly. But a common cause of the symptoms you describe is a bad start/run capacitor or worse, a failing compressor motor.
Todd said to Roger:
Rpger...not a professional myself but I had the same issue. The motor on my outside unit had worn out to the point that it needed to be replaced. Forturantely for me it was under warranty from a unit that I purchase 4-5 years ago. This might be strange for most units but we've had some above average summers here in Texas the last couple of years.
Question: does it help to spray the compressor/condenser coils when it's hot outside?
Does it help to spray water on the compressor coils when the outside air temp. is 100+? The inside air is going up in the afternoon to 82. - Greg Warner 7/7/12
Some readers have reported that their compressor was overheating and ran ok when water cooled - this is perhaps a diagnostic step but not a reasonable repair. And don't soak electrical components.
Question: oil in the capillary tube? - recurrent cap tube clogging
i have replaced my compressor from company and when i started it was giving cool air but the copper pipe out side (large) was not cool enough and after 40 mints its timer light flashes and after 10 more mints its down automatically. it happens again and again i sent back it to company technician is looking into it. He said oil was in capillary and it needs flushing so he will replace its capilary since after cleaning its not fixed. do u think there is no fault in compressor? or what possibly is the problem.. - Wagar 7/11/12
You'll want to check the installation manual to find the control light decoding for your brand and model of cooling equipment. Could be a control or control board problem too. It's just about impossible to flush a cap tube so replacement is normal. But if there is debris in the system, or excessive oil, the new cap can clog as well; good practice would be to empty the system, pull a vacuum, flush the whole system, install a filter dryer, replace the cap tube, and recharge.
Question: A/C not cooling, condenser fan not running
Several days ago I noticed that even though my air handeler was rinning the AC was not cooling, I foudn that the condensor was not turning, I flipped the breaker (that apprered to be in the on position) and it worked for awhile. 15 minutes later I noticed that the condenser was not operating again so I flipped the breaker again it corrected the problem. I then went on the replace the breaker which seemed to correct the problem, the AC worked normally for several days. Now I find the condenser is not working again and flipping the breaker fails the correct the problem. When the condenser was working it was providing good normal cool air. The system is 2 years old. I assume I have an electrical problem in the condenser. What is likely to cause this problem and how can I test for it (I have a test meter) but I want to be careful because I know that a coil can retain a dangerous electrical charge even when all power is off and disconnected. - Rick 7/13/12
typically we see if the fan spins, if it has power, and if the controls and fan contactor are bringing power to the fan when the condenser unit starts up.
My problem turned out to be a bad contacter (damaged by ants) - Rick 7/13/12
Question: loud cricket chirping sounds at the compressor/condenser unit, and slow starting
outside unit making loud cricket sounding noise when running. Takes long time to come on when temp set low. - JT 7/276/12
JT our link at Related Topics NOISE AIR CONDITIONER / HEAT PUMP provides noise diagnostics.
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